The present invention relates to an apparatus and method for controlling an actuatable occupant restraint device for a vehicle. More particularly, the present invention relates to a method and apparatus for controlling an actuatable occupant restraint device having a plurality of sensor inputs.
Actuatable occupant restraint systems, such as air bags and seat belt pretensioners, for vehicles are well known in the art. Such restraint systems include one or more collision sensing devices for sensing vehicle crash acceleration (vehicle deceleration). Air bag restraint systems further include an electrically actuatable igniter, referred to as a squib. When the collision sensing device senses a deployment crash event, an electrical current of sufficient magnitude and duration is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
Certain known collision sensing devices used in actuatable occupant restraint systems are mechanical in nature. Still other known actuatable occupant restraint systems for vehicles include an electrical transducer, such as an accelerometer, for sensing vehicle crash acceleration. Systems using an accelerometer as a crash or collision sensor further include some circuitry, e.g., a controller, for monitoring the output of the accelerometer. The accelerometer provides an electrical signal having an electrical characteristic indicative of the vehicle""s crash acceleration. The accelerometer is operatively connected to a controller, such as a microcomputer, which discriminates between a deployment and a non-deployment crash event by applying a crash algorithm to the acceleration signal. When a deployment crash event is determined to be occurring, the restraint is actuated, e.g., an air bag is deployed and/or a seat belt pretensioner is actuated.
One particular type of occupant restraint system known in the art is a multi-stage occupant restraint system that includes more than one actuatable stage associated with a single air bag. In a multi-stage air bag restraint system, air bag inflation is the result of the control of a multi-stage inflator. Such multi-stage air bag systems typically have two or more separate sources of inflation fluid controlled by actuation of associated squibs. Known control arrangements control the actuation of the multiple stages based on a timer function.
U.S. Pat. No. 3,966,224 is directed to a multi-stage air bag restraint system having two squibs. Under certain types of crash conditions, a first stage is actuated followed by actuation of a second stage a predetermined time after actuation of the first stage. If the crash acceleration is greater than a predetermined level, both stages are simultaneously actuated.
U.S. Pat. No. 4,021,057 is directed to a multi-stage air bag restraint system having a plurality of squibs for gas generators. Crash velocity is compared against a plurality of threshold values for control of the plurality of squibs and, in turn, control of the inflation rate of the air bag.
U.S. Pat. No. 5,400,487 is directed to an air bag restraint system having a plurality of separately controlled gas generators actuated at selected times in a selected order to control the air bag""s inflation profile. The selective triggering is a function of both the detected crash type extrapolated from past received acceleration data and the occupant position based on received occupant position data.
U.S. Pat. No. 5,411,289 is directed to an air bag restraint system having a multiple level gas generating source. The electronic control unit is responsive to a combination of sensed inputs from the temperature sensor, the seat belt sensor, and the acceleration sensor for determining both an optimum gas generation level and inflation sequence times for controlling the multiple level gas generation source.
U.S. Pat. No. 5,626,359 is directed to an air bag restraint system which controls the amount of inflation fluid that flows into the air bag. A controller provides a control signal based on at least two sensed parameters to vent a portion of the available inflation fluid away from the air bag to achieve a desired level of inflation.
Many types of crash algorithms for discriminating between deployment and non-deployment crash events are known in the art. Algorithms typically are adapted to detect particular types of crash events for particular vehicle platforms. One example of such an algorithm is taught in U.S. Pat. No. 5,587,906 to McIver et al. and assigned to TRW Inc.
Air bag restraint systems are also known to require more than one sensor for detection of a deployment crash event. Often, the plural sensors are arranged in a voting scheme in which all the sensors must xe2x80x9cagreexe2x80x9d that a deployment crash event is occurring before restraint actuation is initiated. In certain known arrangements having a first and second sensor, the second sensor is referred to as a xe2x80x9csafing sensor.xe2x80x9d Air bag actuation occurs only if the first sensor and the safing sensor indicate a deployment crash event is occurring.
The present invention is directed to an apparatus for controlling actuation of at least one actuatable protection device. The apparatus includes a first sensor input effective to receive a first sensor signal having a value indicative of a first condition of an occupant of the vehicle seat. The apparatus also includes a second sensor input effective to receive a second sensor signal having a value indicative of a second condition of the occupant of the vehicle seat. The apparatus is operative to determine a default value for the value of the first sensor signal upon determining that the value of the first sensor signal is not within an expected range of values. The apparatus is operative to provide a control signal to control actuation of the at least one actuatable protection device. The control signal has a value that varies as a function of the value of the received second sensor signal and at least one of the value of the received first sensor signal and the determined default value of the first sensor signal.